1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method to form a resist pattern on a target substrate (to-be-processed substrate) such as a semiconductor wafer by immersion exposure, and more particularly, to a semiconductor device manufacturing method which improves the cleaning process before and after the developing process. The present invention also relates to a substrate processing apparatus used for the above-described semiconductor device manufacturing method.
2. Description of the Related Art
Along with the recent advance in micropatterning of a semiconductor device, various kinds of lithography techniques are now under study. An immersion exposure method has received a great deal of attention as the next generation lithography (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 57-153433). This immersion exposure method increases the refractive index of a medium fluid which occupies the optical path between a projection lens and a resist film as the exposure target. This increases the critical angle of the projection lens on the downstream side of the optical axis. Hence, this method enables to project light diffracted by a micropattern below its resolution limit, unlike exposure using air as an optical medium. The mainstream of an immersion exposure apparatus which is now under development is a type (partial immersion exposure apparatus) which fills only the optical path between a resist film and a projection lens and the peripheral portion of the optical path with liquid immersion fluid as medium.
Unfortunately, the following problems may occur in an immersion lithography step using a partial immersion exposure apparatus.
(A) Interaction Between Liquid Immersion Fluid and Substrate
Since a liquid immersion fluid comes in direct contact with the substrate, the constituent components or surface absorbate of the resist film sometimes elute to the liquid immersion fluid. A PAG (and/or photo-generated acid) in the resist, a quencher, or an amine from the substrate deteriorates the final element of the projection optical system, which is in contact with the liquid immersion fluid. Additionally, some metal impurities may influence the lens. For this reason, there is a proposal for, e.g., changing the type of resin of a resist film, a PAG as an eluting additive, a quencher itself, or the solvent of a resist chemical solution.
On the other hand, there is a proposal for forming a cover material film on the upper layer of a resist film to suppress elution from the resist film. The cover material film is formed by spin coating, like the resist film. The cover material film is of a solvent removal type, typically, TSP-3A manufactured by TOKYO OHKA KOGYO or a developer-soluble type which dissolves to a developer of resist.
(B) Followability of Liquid Immersion Fluid Held in the Pattern Exposure Through Wafer Edge Portion.
When exposing each exposure area of the substrate edge portion, a shower head and an liquid immersion fluid held in it pass through the substrate edge portion. At this time, the liquid immersion fluid held between the shower head and the wafer may not completely follow the movement of the wafer stage. Consequently, air bubbles may be trapped in the shower head and produce a lens effect or flare, generating a pattern defect. To the contrary, the liquid immersion fluid may remain on the step of the substrate edge portion, generating a defect due to a watermark. In an extreme case, the movement of the liquid immersion fluid in the shower head may become uncontrollable. This may worsen the controllability of the portion in question in the height direction of the wafer stage, generating a pattern defect due to poor focus controllability.
Forming no step by an edge rinse on the substrate edge portion of the resist film or cover material film which exists on the uppermost layer is obviously advantageous to assure the followability of the liquid immersion fluid described in (A). However, when the resist film or cover material film is formed on the substrate edge portion, especially, up to the vicinity of the side surface of the bevel portion and remains even after resist pattern formation, the processed states of substrate edge portions vary. This leads to generation of dust or an unintended step for the substrate bevel portion.
As described above, in a method of forming a resist pattern by conventional immersion exposure, even though the presence of a resist film or cover material film of the substrate edge portion, which exists on the uppermost layer is advantageous to assure the followability of the liquid immersion fluid, the processed states of substrate edge portions vary. This leads to generation of dust or an unintended step for the substrate bevel portion.
Note that the prior art of the present invention is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 57-153433, W. Hinsberg etc, Proc. SPIE vol. 5376, pp. 21-33 (2004), and J. Talylor etc, Proc. SPIE vol. 5376, pp. 34-43 (2004).